In AML tumor populations, there is strong evidence that a small population of leukemic stem cells (LSCs) gives rise to Clonogenic Leukemic Progenitor (CLPs) lacking self-renewal ability, but which further differentiate into leukemic blast cells. This parallels the normal hematopoietic cellular hierarchy (Figure 1). Post-mitotic blast cells comprise the major bulk of AML tumors. The origin of LSCs is not understood, although some evidence exists that they arise by acquisition of self-renewal ability in MPPs that have presumably inherited mutations from an HSC. In addition to being progenitors for more differentiated cells that comprise the bulk of AML tumors, LSCs can be transplanted to another host, resulting in formation of a new tumor. For preliminary results (see Section N4.2), we prospectively isolated and purified cell populations from stages of myeloid development, as well as from the AML tumor hierarchy. Using breakthrough single-cell technologies, we will dissect the AML LSC population. By applying novel experimental and computational approaches, our aim is to understand the role of differentiation in AML, and how self-renewal is established and maintained.